Abstract

Vitamin D plays a major role in various physiological functions and body homeostasis. The aim of this study was to examine the relationship between serum 25-hydroxyvitamin D status with lung functions and Fractional Exhaled Nitric Oxide (FeNO). 113 (55 males and 58 females) apparently healthy participants were recruited. Participants were divided into two main groups based on their gender and vitamin D levels. Group 1 included male participants categorized according to deficient vitamin D level <30 ng/ml (n=35) and sufficient vitamin D level 30-80 ng/ml (n=20). The second group included 58 female participants with deficient vitamin D level <30 ng/ml (n=19) and sufficient vitamin D level 30-80 ng/ml (n=39). Vitamin D was measured by chemiluminescence immunoassays technique, lung Function parameters were recorded by using an electronic spirometer and Fractional Exhaled Nitric Oxide (FeNO) was measured by using Niox Mino. No association of vitamin D levels was found with reduced lung functions and FeNO levels.

Introduction

Vitamin D is a steroid vitamin that plays a major role in
various physiological functions and body homeostasis. It has
an immune-modulatory and anti-inflammatory effect [1]. The
prevalence of vitamin D deficiency is increasing globally even
in the countries near the equator where sun exposure is high
[2]. Vitamin D deficiency has been recognized as a major
public health problem worldwide [3]. Vitamin D deficiency is
becoming an endemic in many parts of the world and its
deficiency can cause various health problems and poses a great
threat to human health. Vitamin D deficiency has been
associated with various autoimmune, inflammatory disorders
and malignancy [4] and has also been linked to respiratory
illness including asthma and chronic obstructive pulmonary
disease. Recent reports suggest that vitamin D deficiency is
associated with impaired ventilatory functions [4,5]. However,
there is a dearth of research reports confirming a relationship
between vitamin D and lung function.

Spirometry and Fractional Exhaled Nitric Oxide (FeNO) are
mainly important in various clinical and occupational settings
[6,7]. Lung functions in addition to Fractional Exhaled Nitric Oxide in subjects with an association of Vitamin D have not
been collectively and extensively studied. Therefore, the aim of
this study was to investigate the association of serum 25-
hydroxy vitamin D with lung function and Fractional Exhaled
Nitric Oxide.

Subjects and Methods

Subject selection

This cross sectional study was conducted in the Department of
Physiology, College of Medicine, King Saud University,
Riyadh, Saudi Arabia. For this study, 113 (55 males and 58
females) apparently healthy participants, with mean age range
18-60 years were recruited. Participants were divided into two
main groups based on their gender and vitamin D levels. Group
1 included 55 male participants categorized according to
vitamin D levels, namely; deficient vitamin D level <30 ng/ml
(n=35) and sufficient vitamin D level 30-80 ng/ml (n=20).
Group 2 included 58 female participants categorized according
to vitamin D levels, namely deficient vitamin D level
<30 ng/ml (n=19) and sufficient vitamin D level 30-80 ng/ml (n=39). All the subjects were matched for age, weight, height,
ethnicity and socioeconomic and demographic status. A
comprehensive clinical history of each subject was takes to
decide whether to include in the research or not.

Exclusion criteria

Subjects with identified cases of anaemia, blood diseases,
diabetes mellitus, bronchial asthma, malignancy and drug
addicts were excluded from the study. Subjects who smoked
cigarette or shisha were also excluded from the study [7,8]. We
also excluded the subjects whose serum vitamin D was more
than >80 ng/mL to minimize the vitamin D toxicity effect.

Potential confounders

The potential confounding factors were carefully considered
due to their known or plausible associations with impact and
outcomes. These factors include age, gender, ethnicity, height,
weight, health status, socioeconomic position and outdoor
activity.

Measurement of 25 (OH) vitamin D

For the determination of serum 25 (OH) vitamin D
concentrations, about 5-6 ml of blood was obtained from each
participant by vein puncture method. Serum 25 (OH) vitamin
D levels were measured in nmol/L by using direct
chemiluminescence immunoassays (LIASON-Diasorin) [9]. It
is commonly used for the determination of 25 (OH) vitamin D
in serum or plasma [10]. It has an excellent detection range
[11], and is a valid tool for the determination of serum 25 (OH)
vitamin D concentrations [12].

Spirometry

The ventilator lung function parameters were measured by
using an electronic spirometer SPIROVIT SP-1 (Schiller,
Switzerland). Lung function test parameters were recorded
including Forced Vital Capacity (FVC), Forced Expiratory
Volume in first second (FEV1), Forced Expiratory Ratio
(FEV1/FVC%), Peak Expiratory Flow (PEF), Forced
Expiratory Flow 25% (FEF-25%), Forced Expiratory Flow
50% (FEF-50%) and Forced Expiratory Flow 75% (FEF-75%).
The established techniques in performing the various lung
function tests for this study were based on American Thoracic
Society of Standardization [13].

Fractional Exhaled Nitric Oxide

The Fractional Exhaled Nitric Oxide [FeNO] was determined
by using a Niox Mino, Aerocrine, Solna and Sweden. The
FeNO device was pre-calibrated and programed for 300
measurements. Tests were recorded at a fixed time of the day
to minimize the diurnal variation. The established procedures
in performing FeNO test was based on the American Thoracic
Society/ERS Standardization procedures [14]. The design and
execution of this study was approved by the Institutional
Review Board, Department of Family and Community
Medicine, College of Medicine, King Saud University, Riyadh, Saudi Arabia and informed consent was obtained from all the
study participants.

Statistical analysis

The data were entered into the computer and analysed by using
the Statistical Package for Social Sciences [SPSS for Windows,
version 21.0]. Unpaired student’s t-test (parametric test) was
applied to test the difference in the means between the
variables. The level of significance was considered at p<0.05.

Table 2. Comparison of anthropometric, lung function and FeNO
between the female subjects with sufficient and deficient levels of
vitamin D.

Table 3 summarizes the correlation between lung function
parameters, Fractional Exhaled Nitric Oxide and vitamin D
between the male and female subjects with sufficient and
deficient vitamin D levels. There was a no significant
difference in various parameters between the groups (Table 3).

Discussion

The prevalence of vitamin D deficiency is increasing globally
and has been linked to various health problems. In the present
study, we examined the relationship of serum 25-
hydroxyvitamin D status with lung functions and Fractional
Exhaled Nitric Oxide (FeNO) in Saudi adult community, but,
we did not find any association of serum 25-hydroxy-vitamin
D with impaired lung function and Fractional Exhaled Nitric
Oxide. Previously, Thuesen et al. 2015 [15] reported that 25
(OH) vitamin D levels do not influence the development of
asthma and allergy among adults. Moreover, their results did
not support the notion that 25 (OH) vitamin D levels are
associated with lung function impairment. Similarly, Berg et al.
2013 [16] conducted a study on the association of Vitamin D
and vitamin D binding protein (DBP) with COPD and FEV1.
They found that 25 (OH) vitamin D was not associated with
DBP and DBP was not associated with FEV1.

Lange et al. 2012 [17] conducted a study to determine the
effect of vitamin D deficiency and smoking on lung function.
In the overall cohort, they found that, there was no significant
effect of vitamin D deficiency on lung function or on lung
function decline. Although, among smokers, vitamin D
sufficiency appeared to have a protective effect on lung
function and the rate of lung function decline, modifying the
effect of smoking. Furthermore, Shaheen et al. 2011 [18]
determined the possible role of serum 25 hydroxy vitamin D in
respiratory disease and lung function. They found that total
vitamin D intake was positively associated with forced
expiratory volume in 1 s (FEV1). However, serum 25 (OH)
vitamin D concentrations were not related to FEV1. Their
findings did not confirm a positive association between serum
25 (OH) vitamin D concentrations and lung function. In the
present study, we did not find an association between vitamin
D concentration with pulmonary functions and FeNO. The
present study findings are in consistent to the results from
previous studies Thuesen et al. 2015 [15]; Berg et al. 2013
[16]; Lange et al. 2012 [17]; Shaheen et al. 2011 [18].

In contrast, Khan et al. [19] conducted a cross-sectional study
and found a significant association between vitamin D levels
and some pulmonary function variables FVC and FEV1,
especially in overweight or obese men but they did not observe
a notable influence of vitamin D deficiency on pulmonary function among women. However, in the present study, we did
not find any association between the lung function parameters
and Vitamin D concentration. The most probable reason for
this contradiction is that, in our study the entire sample size
was well matched for age, gender, height, weight, ethnicity and
socioeconomic status, however, Khan et al. [19] found the
association mainly in the obese men and they did not observe
any influence of vitamin D deficiency on pulmonary function
in women. It is well established fact that obesity impairs the
lung function Melo 2014 [20]; Davidson et al. 2014 [21]. We
believe that, the lung function impairment might be the effect
modifier of obesity rather than vitamin D levels. In another
study, Semba et al. 2012 [22] reported that serum 25 (OH)
vitamin D was associated with poor pulmonary function in
older disabled women. The findings of the present study are in
contradiction to Semba et al. 2012 [22]. As they have
conducted the lung function in older and disabled women. The
most probable reason for poor lung function is old age and
disability. It is established fact that lung functions are
decreased in old age and among disabled people [23]. Yao et
al. 2014 [24] investigated the relationship of vitamin D status
with lung function and FeNO in a children. They found a no
significant association between serum 25 (OH) vitamin D
levels and FeNO after adjusting for confounders. Similarly in
the present study we did not find an association between
vitamin D levels and FeNO.

Study strengths and limitations: This study has several
strengths. Most notably, it was the first study to explore the
relation between the lung functions, FeNO and vitamin D
status. The analysis included age, height, weight, ethnicity and
socioeconomically matched subjects. All of the Spiro metric,
FeNO and Vitamin D measurements were carried at the fixed
time of the day to minimize the diurnal variation.

One of the limitations of the present study is its cross-sectional
nature that hampers to establish cause-and-effect relationships
among pulmonary function, FeNO and vitamin D. The second
limitation of the present study was a small sample size
therefore; we suggest that in future large sample sized studies
should be conducted to reach at the better conclusions. The
third limitation of the current study was that the vitamin D
concentration was measured only once for each participant. It
is known that there is seasonal fluctuation in 25 (OH) vitamin
D concentrations, with lower concentrations in the winter time
because major percentage of vitamin D is acquired from
exposure to sunlight [25]. Therefore, the measurement
recorded was not a meaningful representation of the
individual's average vitamin D concentration throughout the
year. In addition, we did not know the (dietary and sunlight)
habits of the participants over the previous 3-4 weeks before
the collection of the blood for the measurement of vitamin D.
As 25 (OH) vitamin D concentration depends on dietary
intakes and exposure to sunlight [25].

Conclusion

The current investigation concluded that, vitamin D has no
association with lung function impairments and FeNo levels. We suggest that large sample sized lung function studies along
with FeNO measurements should be conducted to find
association with vitamin D to get the better interpretation to
establish the clinical relevance.

Acknowledgement

The authors are thankful to the Deanship of Scientific
Research, King Saud University, Riyadh, Saudi Arabia for
supporting the work through research group project (RGP-VPP
181).